The invention relates to a diffuser and, more particularly, to a diffuser for a centrifugal compressor which is configured to optimize flow distribution to a combustion chamber and which may be manufactured to close tolerances in a manner which assures uniformity between diffusers.
Centrifugal compressors generally include a rotating impeller arranged to accelerate and thereby increase the kinetic energy of a gas flowing therethrough. The diffuser is generally characterized by an annular space surrounding the impeller. The diffuser acts to decrease the velocity of the fluid flow leaving the impeller and thereby increase its static pressure. Prior art diffusers have generally included a plurality of circumferentially spaced passages which converge to the annular space surrounding the impeller. These passages expand in area downstream of the impeller in order to diffuse the flow exiting the impeller. It has been found for diffusers of this type which are to be utilized with gas turbine engines that it is preferable to have the diffuser passages assume an initial circular cross-section so as to accommodate with minimal losses the extremely high flow velocities of the gases exiting the impeller and thereafter gradually merge into a rectangular outlet to minimize losses which accompany flow exiting past a series of blunt edges as is found between a plurality of circular outlet passages. One diffuser of this type is disclosed in U.S. Pat. No. 3,719,430 issued to Blair et al on Mar. 6, 1973, and assigned to the assignee of this invention. The diffuser passages of the Blair et al application are generally conical for their entire length except for a merging section at the outermost radial end of the passage. In order to minimize the lengths, the merging section maintains a uniform cross-sectional area throughout the entire length such that there is no diffusion of flow therethrough. The outside circumferential edges of the diffusers are beveled to produce two converging frustoconical surfaces. Diffusers constructed in accordance with the teachings of the Blair, et al application have demonstrated significant improvements in the performance of centrifugal compressors for gas turbine engines. However, because of the complex geometry of the diffuser passages particularly at the outlet area which includes a merging section of uniform cross-section as well as scalloped edges diffusers of the type disclosed by Blair, et al have been found to be relatively expensive to manufacture and difficult to maintain the close tolerances required to assure uniformity between diffusers. Further, because of the relatively short length of the merging section there is a rather rapid change in the curvature of the walls of the merging section which tends to cause local flow separation with a resulting reduction in diffuser efficiency.
It is therefore the object of the present invention to provide a diffuser for a centrifugal compressor which is configured to optimize flow distribution to a combustion chamber and which may be easily manufactured to close tolerances in a manner which assures uniformity between diffusers.